An internal combustion engine of this kind is known, for example, from U.S. Pat. No. 4,508,070. According to this Patent Specification, the surfaces of the combustion chamber are given a fine surface structure in the form of recesses comprising a multiplicity of grooves or pits, each having a width of up to about 3 microns and a depth of up to about 1 micron. Surfaces treated in this way are said to improve the octane number requirement of an engine by about 5, i.e. an engine requiring e.g., a 98 octane fuel can be driven on a 93 octane fuel. Tests have shown, however, that for reasons not yet fully understood this improvement is not always achieved.
As is well known, subsequent to ignition the flame-front propagates in the combustion chamber at the same time as the un-combusted fuel/air mixture is compressed and heated. If the temperature and the pressure of the non-combusted gas mixture reaches critical values before the characteristic flame-front has passed through the whole of the gas mixture, the non-combusted gas mixture will combust spontaneously and result in combustion knock. Apparently the surface structure is able to influence energy conditions in the combustion chamber in some instances, so as to prevent combustion knock.
It is also possible to increase engine efficiency, and therewith reduce fuel consumption, and to reduce heat losses in a similar manner, as recognised in U.S. Pat. No. 3,459,167. This specification teaches internal combustion engines in which combustion chamber surfaces have been coated with a material which is highly reflective to infrared radiation and which also forms a thermal barrier, so as to keep the walls of the combustion chamber at a relatively low temperature. The coating may have the form of a layer of cuprous oxide, and is applied by first cleaning the surface or surfaces to be treated and then blasting said surface (surfaces) to create irregularities therein. The cuprous oxide layer is then applied, e.g., by flame spraying copper particles to a thickness of at least 0.15 mm. In this way there is provided a coating which is at least 75% reflective to thermal radiation within a wave length of 0.7-10 microns at prevailing combustion chamber temperatures.